Unwanted line revealed during Cycles Render
It's likely due to the fact that you used a boolean to make the wall. Booleans are notorious for ugly topology - for example, blender works best with quads (faces with four vertices only) and any more vertices (n-gons), or any less (tris), will often cause shading errors. That being said, take a look any of the (single) faces that makes up the door in your image - how many vertices can you count on those faces?
The solution in many cases, is to use a simpler object for your Boolean, which makes it easier to connect loose vertices manually. If you need things to be round, you can &quot;round things out&quot; using a Subdivision Surface Modifier and/or Smooth Shading if necessary.
In the image below, the &quot;wall&quot; on the left is made using a cylinder with 8 faces as the cutout object, and the wall on the right uses the default 32 face cylinder as the cutter.

Since the 8 sided cylinder leaves a much more workable number of new (extra) vertices, it is a trivial matter to connect them to the rest of the mesh in a manner that leaves only quads. Because of this, I was able to apply a Subdivision Surface modifier and Smooth Shading without incident.
While the wall on the right is technically capable of being connected in such a way that it leaves only quads, the sheer number make it a time consuming effort, and will leave your mesh much more subdivided than it originally was. Because of this, I left it in it's fresh post-boolean state (without making quads) to demonstrate why it's necessary. The topology is so bad that I cannot use a Subdivision Surface Modifier without serious mesh-breaking errors, and so I did not use one. I did Shade Smooth, but you can see the shading errors that are a result of the n-gon faces.
The TLDR is that Booleans leave &quot;poor&quot; topology that often must be connected to the rest of the mesh manually to convert it back to a quad-only state and avoid shading errors. To make the manual connection process easier, use a &quot;cutter&quot; object with as few faces as possible, and do the rest with other modifiers if necessary.